Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. However, the non-planar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Thus, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. During planarization, the substrate is mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a “standard” or a fixed-abrasive pad. A standard polishing pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push the substrate against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad.
The effectiveness of a CMP process may be measured by the CMP process's polishing rate or removal rate. The removal rate is of particular importance with polymer layers on a substrate because of the polymer's hardness after curing. Planarizing a polymer layer can take an hour or more, greatly slowing the throughput of the semiconductor manufacturing processes. The slow removal rate is one of the main factors as to why polymer layers are not normally planarized, limiting the quality and performance of a semiconductor device due to step-height differences on the surface of the substrate.
Thus, the inventors have provided improved methods of planarization of polymer layers on a substrate.